Even at a very young age, eye problems can be discovered with a thorough exam. There are some eye problems that will be detected even at the pre-school exam, 3 to 5-years-old. That if not treated and cared for properly then can lead to life long problems.
The 20-20 letter test may not be the exam that doctors are focusing on lately. They are looking at how the eyes work together, how efficiently they can work up close because so much of the workday in school is close work not board work. So doctors are more concerned with that far-sightedness that a common case of near-sightedness.
In some areas, officials are working to make eye exams made mandatory for students, before the start of school.